Two pipes A and B can fill a tank in 20 and 30 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank ?
Part filled by A in 1 min = 1/20.
Part filled by B in 1 min = 1/30.
Part filled by (A+B) in 1 min = (1/20 + 1/30)
Both the pipes can fill the tank in 12 minutes.
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